The present invention relates to laser gyroscopes employing two ring lasers arranged in two planes, one above the other, and relative to a common reference axis extending perpendicularly to the two planes, which in turn extend in parallel to each other. The two lasers operate independently of each other and do not influence each other. The radiation generating device may be a solid state laser and/or a gas laser, whereby in both instances the resonators of the lasers are constructed as wave guides. An article entitled "The Laser Gyro" by B. J. Kilpatrick and published in "IEEE Spectrum", October 1976, 1967, general background information.
German Patent Publication DAS No. 1,961,121 describes a ring laser device for measuring angular speeds. In this known device the sensitivity for the measuring of small angular speeds is improved and the time required for the measuring is substantially reduced due to the fact that two ring lasers which are independent of each other are arranged in two planes one above the other. Each of these ring lasers is equipped with electro-optical elements in such a manner that the waves in each of the two ring lasers can travel only in one direction. Since the two lasers of this known device work independently of each other, the device avoids the so called "lock-in" effect. However, such effect may occur where the resonance frequencies, which are shifted due to the rotation and which are located very close to each other, effectively oscillate with a common frequency. Thus, as the result of the so called lock-in effect, it is not possible to produce a difference frequency as the result of the rotation. As mentioned, the device according to German Patent Publication No. 1,961,121 avoids the so called lock-in effect. However, the known apparatus has the disadvantage that the paths or trajectories of the two travelling waves propagating or moving in opposite directions are not automatically equal to each other. Moreover, the length of these paths or trajectories varies with time due to thermal deformations of the materials of which the resonators are made. Thus, the differences in the lengths of these trajectories also vary with time. For these reasons it is not possible to achieve a measuring result free of faults.
German Patent Publication DOS No. 2,044,575 discloses a similar laser gyro in which two independent, linear lasers are arranged in the same plane, but in an opposite sense in order to achieve measuring times which are as short as possible. Each of the two lasers shows up a Doppler-broadening which is different of the one of the other and each of the emitted beams travels only through the path of a half-ring interferometer. Thus, here again a measuring result free of faults cannot be achieved.
Substantially all prior art gyros use HeNe-lasers constructed in a ring configuration and achieve a sensitivity of a few arc seconds, whereby the dimensions are typically within the range of three to fifteen centimeters and wherein the continuous duty drift is within the range of 0.003 to 10.degree. per hour. However, in order to achieve this type of precision and sensitivity it is necessary to use optical elements of the highest precision. In addition, it is necessary to employ a plurality of complicated compensating techniques, as well as to take into account predetermined allowances.